Table 1: Antimicrobials in the gastrointestinal tract.

Antimicrobial peptideChromosomal locationMolecular mass (kDa)Secretory stimuliDistribution in gastrointestinal tractBiological functionChanges in inflammatory bowel disease

hBD-18p23.13.5–4.5Constitutive in epithelial cells, IFN-γ and LPS in monocytesUbiquitous in epithelial cells of small and large intestine, monocytes, monocyte-derived dendritic cellsAntimicrobial, chemotacticReduction in colonic IBD

hBD-2, 3, 48p23.13.5–4.5LPS, flagellin mediated by NF-κB and AP-1Epithelial cells, monocytes- Antimicrobial, chemoattractant for macrophages and monocytes, - hBD-2: mast cells and neutrophils- Attenuated induction observed in colonic CD- Reduced copy numbers for hBD-2 in colonic CD

HD-5 and HD-68p23.13.5–4.5NOD2 activation (MDP, LPS) TLRGranules of ileal Paneth cells (also metaplastic Paneth cells in other areas of intestinal tract)Antimicrobial, induction of IL-8- Reduction in ileal CD, more pronounced in patients with NOD2 mutation- HD-5 and HD-6 expression due to metaplastic Paneth cells in UC and CD colon

Cathelicidin (“LL-37”)3p21.318Butyrate, vitamin D, bile acids, MDPEpithelial cells, leukocytesAntimicrobial, chemotactic- Attenuated induction in colonic CD- Ileal CD and UC show regular induction

Elafin20q13.129.8IL-1, TNF-αEpithelial cells, leukocytesAntiprotease with antimicrobial and chemotactic propertiesAttenuated induction in colonic CD

Secretory phospholipase A216p13.1–p1214LPSEpithelial and inflammatory cells, Paneth cell granules- Acute phase protein involved in eicosanoide metabolism- Small intestinal mucosal defense?

Lysozyme12q1516.5?Gastric, pyloric and duodenal glands, small intestine, macrophages and monocytes, not in colonic tissueAntimicrobial against Gram-positive bacteria, chemotactic- Small intestine: no changes observed - Increased colonic expression due to metaplastic Paneth cells

BPI (bactericidal/permeability-increasing protein)20q11.2350LPSEpithelial cells, neutrophilsAntimicrobial, binds LPS-compoundsNo changes observed, regular induction in IBD